Utilize ultrasonic energy to reduce the initial contact forces in known-good-die or permanent contact systems

ABSTRACT

A machine and method for bonding puncture-type conductive contact members of an interconnect to the bond pads of a bare semiconductor die includes the use of one or two ultrasonic vibrators mounted to vibrate one or both of the die and interconnect. A short axial linear burst of ultrasonic energy enables the contact members to pierce hard oxide layers on the surfaces of the bond pads at a much lower compressive force and rapidly achieve full penetration depth.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/921,622, filed Aug. 3, 2001, pending, which is a divisional ofapplication Ser. No. 09/416,248, filed Oct. 12, 1999, now U.S. Pat. No.6,296,171 B1, issued Oct. 2, 2001, which is a continuation ofapplication Ser. No. 09/027,690, filed Feb. 23, 1998, now U.S. Pat. No.6,045,026, issued Apr. 4, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to electrical connections tosemiconductor devices. More particularly, the invention pertains tomethods and apparatus for making nonpermanent and permanent lowresistance interconnections between a semiconductor device (die) and asubstrate.

[0004] 2. State of the Art

[0005] As the densities of input/output (I/O) wire bond pads increase onsemiconductor devices, testing of the devices becomes more difficult.The function of any interconnect system, whether a probe card, testsocket, or burn-in socket, is to provide a reliable interconnect betweenthe integrated circuit tester and the individual semiconductor device.The reliable burn-in and testing of bare dice is required to provideknown-good-die (KGD) for incorporation into multi-chip assemblies, forexample. The KGD testing of dice and wafers is dependent upon uniformlyachieving consistent electric connections between the test apparatus andthe semiconductor device substrate.

[0006] Prior art contact members for testing dice are generally of fourforms. In one form, the contact members simply abut the bond pads orleads and the two are pressed together to make the desired electricalcontact. Examples of this type of interconnection are described in U.S.Pat. Nos. 5,406,210 of Pedder, 5,572,140 of Lim et al., 5,469,072 ofWilliams et al. and 5,451,165 of Cearley-Cabbiness et al.

[0007] A problem with such connections is that bond pads are typicallycovered with a layer of metal oxides or silicon dioxide which insulatesthe pads and makes simple contact ineffective as a reliable electricalconnection. In some cases, differential thermal expansion of the contactmember may cause lateral movement which tears the bond pad.

[0008] In a second configuration, contact members may be formed to makea “wiping action” contact with the bond pads. Examples of such arevarious sockets, pins, plugs, etc. Again, as is well known in theindustry, pre-existent oxides and subsequently-formed oxides on themetal surfaces result in defective electrical contact.

[0009] In a third form of making temporary contact between a test deviceand a die, the contact members are non-permanently bonded to the pads onthe dice by a solder or other conductive bonding material. Illustrativeof this configuration is the disclosure of U.S. Pat. No. 5,517,752 ofSakata et al. Removal of the solder (by remelting) is required todisconnect the contact members from the dice after testing is completed.

[0010] The use of solder reflow technology for temporary bonds has manydisadvantages including the following. First, surface preparation withhighly corrosive and environmentally hazardous fluxes is required.Second, solder bonds are occasionally defective, requiring testing ofeach bond and reworking if necessary. Third, solder reflow requiresseveral additional processing steps and apparatus, adding to themanufacturing expense. Fourth, the temperatures required for reworkingas well as disconnect melting place additional stresses on the device.

[0011] A fourth form of contact member is configured to puncture a bondpad, passing through an oxide layer into the underlying metal forlow-resistant electrical contact. An example of this configuration isshown in U.S. Pat. No. 5,506,514 of Difrancesco, incorporated byreference herein.

[0012] One preferred form of a puncturing contact member is described inU.S. Pat. Nos. 5,326,428 of Farnworth et al., 5,478,779 of Akram, and5,483,741 of Akram et al., all of which are incorporated by referenceherein. In this configuration, the interconnect has a non-conductive orsemiconductive substrate upon which raised contact members include sharpprojections for puncturing the metal oxide coating on the bond pads andretaining non-permanent, low-resistance electrical continuity with theunderlying metal. A compressive force is maintained during the time thedie or dice are undergoing testing. The sharp projections may be formedto limit the penetration distance.

[0013] Generally, the metal oxide layer overlying the metal is muchharder than the metal. Thus, the force required to penetrate and passthrough the oxide layer is considerably greater than the forces requiredto penetrate the metal.

[0014] The compressive force exerted on the interconnect and thesemiconductor die may be controlled by (a) controlling the rate ofmovement toward each other, or (b) controlling the compressive forceitself, such as with a spring or other such device. In either case, theinitially high resistance requiring a high compressive force topenetrate the oxide layer is suddenly released upon penetration.However, the compressive force may not be reduced quickly enough toavoid “over-penetration” of the underlying metal. Furthermore, evensmall differences in the thickness of the oxide layer will result inoxide penetration at different compression levels. The requiredcompressive force to achieve oxide penetration of all bond pads willvary from die to die, further exacerbating the problem. Such isparticularly a problem where the die has a large number of bond padsthereon and the compressive force required to penetrate any oxidecoating on the bond pads is larger than that capable of beingtransmitted through the head of the transfer apparatus.

[0015] As is well known in the art, ultrasonic vibration has been usedto join bond pads and leads with thin wires. U.S. Pat. Nos. 5,494,207and 5,607,096 of Asanasavest and U.S. Pat. No. 4,475,681 of Ingle teachparticular ultrasonic wire bonding apparatus and methods. Ultrasonicvibration may be combined with heating as in the “thermosonic” wirebonding process. U.S. Pat. No. 3,697,873 of Mazur describes a method forultrasonically soldering contacts and indicates that “the ultrasonicwave energy acts to break up oxides on the surface of the semiconductorbody . . . ”

[0016] U.S. Pat. No. 3,938,722 of Kelly et al. discloses an apparatususing ultrasonic energy for forming bonds between beam leads andconductive surfaces such as on a substrate.

SUMMARY OF THE INVENTION

[0017] The invention comprises an apparatus and method for reducing thecompressive force required to achieve the desired initial penetration ofa bond pad by a contact member, such as used in a die burn-in andtesting carrier. The high initial force required in the prior art tobreak through the “crust” of hard oxide on the surface of the metal padis much reduced. Penetration of the hard oxide layer ordinarily resultsin a sudden “rebound” of accelerated movement due to reduced resistance,and the contact member may overpenetrate the bond pad. However, withthis invention, the rebound is minimized, if not eliminated.

[0018] The maximum compressive force required to achieve the finaldesired penetration of the bond pad is also reduced, while ensuring thatall of the bond pads on a bare die are fully penetrated to provideuniformly low resistivity interconnections.

[0019] In the invention, ultrasonic vibration is applied to either oneor both of the bare die and the corresponding interconnect contactmember. The vibratory movement is generated in a direction generallyperpendicular to the die surface by a transducer including e.g. apiezoelectric element. This direction of vibratory movement is knownherein as the “axial” direction.

[0020] The frequency and amplitude of the vibratory forces arecontrolled such that the interconnect contact member pierces the hardoxide layer on the bond pad very rapidly and at lower appliedcompression forces. The ultrasonic vibration also ensures that all bondpads are fully penetrated to achieve low-resistivity connections.

[0021] The bonding system of the invention permits the use of lowbonding compressional forces together with generally unidirectionalultrasonic vibrational energy and a frequency modulated controlledresonance to produce uniformly reliable simultaneous connection of allbonds on a die without heat or with minimal heating.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022] The invention is illustrated in the following figures, whereinthe elements are not shown to scale.

[0023]FIG. 1 is a cross-sectional end view of a bonding apparatus of theinvention in an assembler machine;

[0024]FIG. 2 is an enlarged cross-sectional view of contact members of asemiconductor device and an interconnect test apparatus prior to bondingof the contact members with the method and apparatus of the invention,as found within area 2 of FIG. 1;

[0025]FIG. 3 is an enlarged cross-sectional view of contact members of asemiconductor device and an interconnect test apparatus followingbonding of the contact members with the method and apparatus of theinvention; and

[0026]FIG. 4 is a generalized graphical depiction of the bond padpenetration as a function of applied force with and without theultrasonic vibration of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] An improvement in forming a non-permanent or permanentlow-resistivity electrical connection between a penetration-type raisedcontact member and a conductive bond pad of a bare die is describedherein. The invention is particularly applicable to systems for testingbare dice to be referred to as known-good-dies (KGD), where the testinginterconnect is re-used many times.

[0028] The invention is described herein in relation to a testingapparatus or assembler whereby one or more bare dice (singulated or in awafer form) are non-permanently interconnected with a test device, butthe invention may be used for making other temporary or permanentelectrical connections between a bare die and a substrate with anydesired type contact member or a puncture-type contact member.

[0029] As depicted in FIG. 1, an assembler machine 10 is shown in partand includes a die mount or quill 12 to which a bare die 14 is securedon its back side 16 by a vacuum formed through apertures 18 of the quill12. The vacuum may be applied either through one aperture 18, aplurality of apertures 18, a quill 12 having a metallic tip, a quill 12having a resilient tip, or variations thereof. The active surface 20 ofthe die 14 is shown with a plurality of bond pads 22 for connection touseful electronic circuits, as known in the art. Facing the activesurface 20 of the die 14 is an exemplary interconnect 24 including asubstrate 26 having a connection surface 28 with a plurality of raisedcontact members 30. The contact members 30 are located on the connectionsurface 28 for accurate contact with corresponding bond pads 22 on theactive surface 20.

[0030] The interconnect 24 is here exemplified as a die tester, i.e. adie carrier used for burn-in and testing of dice for KGD purposes or a“probe card” used for testing purposes, having its rear side 38 mountedon a support member 32 by any suitable means 34 extending between theinterconnect 24 and the support member 32. Alternative methods ofmounting the interconnect 24 and/or die 14 include mechanical retainingmembers and the like as known in the art.

[0031] The quill 12 supports the die 14 and may be lowered in axialdirection 40, i.e. parallel to centerline 42, whereby the die andinterconnect 24 meet and are electrically joined by a controlledcompressive force in direction 40. The term “interconnect 24” is usedherein as being a generic term for any device having contact members 30which are simultaneously connected to the bond pads 22 of a die 14. Themachine 10 may include means for controlling the positions of the die 14and interconnect 24 by optical, optical-mechanical or other methods forvertical alignment and parallelism.

[0032] One or more ultrasonic vibration generators or transducers 44 aremounted to vibrate the die 14 and/or interconnect 24 in an axialdirection 45, i.e. parallel to centerline 42. FIG. 1 shows a firstultrasonic vibration generator 44A surrounding and attached to the quill12. The generator 44A is controllable to axially vibrate the quill 12and attached die 14.

[0033] Also shown is a second ultrasonic vibration generator ortransducer 44B underlying support member 32 and controllable to axiallyvibrate the support member 32 and attached interconnect 24. The supportmember 32 is constructed of a material such as metal, e.g. stainlesssteel, which will transmit the ultrasonic vibrational movement withminimal losses in force, linearity or amplitude.

[0034] The second ultrasonic vibration generator 44B may alternativelybe positioned above the support member 32, i.e. adjacent theinterconnect 24.

[0035] The produced vibratory motion is generally a sinusoidal functionof time. The generators or transducers 44A and 44B may be separatelycontrolled to produce differing frequencies and motion amplitudes whichin combination achieve rapid linear axial piercing of the oxide layer 54(FIG. 2) and penetration of the underlying metal 58, and goodlow-resistivity adhesion of the contact member 30 with the metal,without causing damage to any of the bond pads 22 which requires repair.

[0036] Where two generators 44A, 44B are used for vibrating the die 14and interconnect 24, respectively, it is preferred that they be about90-180 degrees out of synchronization, so that the motions of the dieand interconnect are opposed, i.e. alternately toward each other andaway from each other during a fraction of the sinusoidal curves. When180 degrees out of synchrony, the amplitude setting of both transducersmay be minimized.

[0037] In another feature, the amplitudes of the two generators 44A, 44Bare set to differ such that overlapping amplitude portions result invibratory contact of the contact members 30 with the bond pads 22, eventhough the vibrators are in synchronization or minimally out ofsynchronization.

[0038] The generators 44A and/or 44B may be, for example, 25 wattgenerators of about 20-60 KHz frequency, and may be adjustable for F.M.(frequency modulation). Where a single generator 44A or 44B is utilized,the transmitted power controlling the vibrational amplitude is set to avalue whereby the vibrational amplitude may typically be about 5-30percent of the desired full penetration depth. Where two generators 44Aand 44B are used to vibrate both the die 14 and interconnect 24, theamplitude setpoint of each may be reduced somewhat so that the netmaximum amplitude is not excessive. Likewise, the vibratory forcestransmitted to each of the die 14 and interconnect 24 may be reduced toprevent excessive forces acting on the bond pads 22 by the contactmembers 30. The optimal power requirement will vary, depending upon thetotal number of connections to be made, as well as other factors,described infra.

[0039] Non-axial and non-linear vibrations of the die 14 andinterconnect 24 are largely avoided by promoting axial vibrations only,in order to prevent any tearing of the bond pads 22. Any tendency toproduce non-linear or non-axial vibration may be further reduced byrelatively rigid lateral support of the die 14 and interconnect 24, orby other means known in the art. A known ultrasonic generator has afeedback arrangement which reduces non-linearity.

[0040] The time required to achieve full penetration of all bond pads 22is of very short duration, typically of the order of a few milliseconds,e.g. about 5 milliseconds, up to about 200 milliseconds or more,depending upon the design, numbers, sizes and material of contactmembers 30 and bond pads 22. The ultrasonic vibration force(s) andamplitude will also affect the required time of ultrasonic vibration.

[0041] We turn now to FIG. 2, which is an enlarged view of portion 2 ofFIG. 1. Semiconductor die 14 is shown with active surface 20. Bond pads22 are shown mounted on the active surface 20, and the remainder of theactive surface 20 is shown covered with a passivation layer 46.

[0042] For purposes of illustration, raised interconnect contact members30 described in U.S. Pat. Nos. 5,326,428, 5,478,779 and 5,483,741 areused in FIGS. 2 and 3 as exemplary puncture-type contact members towhich the invention is applied. In this embodiment, the contact members30 comprise raised pillars 48 having conductive caps 50 with sharpapexes 52 for piercing a hard oxide layer 54 on a bond pad surface 56and penetrating the underlying conductive metal 58. The design of theapexes 52 results in increasing resistance to penetration as thepenetration proceeds. Although each cap 50 may include a flatpenetration stop surface 60 to limit penetration, over-penetration mayyet occur under circumstances of excessive force or misalignment.

[0043] At full penetration, the apexes 52 are typically retained by themetal 58 of the bond pad 22 to a degree which permits permanent use ofthe interconnect-die combination. Normally, however, the interconnect isa part of a ceramic die carrier for testing an individual die, such asin KGD tests, and only temporary use is made of the connectionsdescribed herein.

[0044] As taught in the patents cited above, the interconnect 24includes conductive traces, not visible in FIGS. 2 and 3, from eachcontact member 30 to a test circuit or other circuit.

[0045] In FIG. 2, the tips 62 of the sharp apexes 52 are shown as justtouching the oxide layer 54 on each bond pad surface 56. In the priormethod of forming an electrical connection, the die 14 was subsequentlycompressed downwardly in direction 40 until the tips 62 pierced the hardoxide layer 54 and then penetrated the softer metal 58 to approximatelythe desired penetration depth. A typical force-penetration curve 64 forthe prior method is shown in FIG. 4. In the prior art method, theexerted compressive force was initially increased to an oxide piercingvalue 66, at which point the resistance suddenly decreased, enabling adecreasingly rapid penetration. The compressive force then increaseduntil the desired “full penetration” depth 70 was attained at forcevalue 68.

[0046] Depending upon the configuration of the system, the prior artforce-penetration curve may be more like that of curve 74, i.e. wherepenetration occurs more rapidly than force reduction. As shown, themomentum of the contact member 30 may carry it to an excessivepenetration value 76.

[0047] It should be noted that in FIG. 4, curve 72 denotes a theoreticalforce-penetration relationship where there is no hard oxide layer 54 onthe bond pad 22, and penetration is through the metal only.

[0048] In the method of the invention, either or both of the die 14 andinterconnect 24 are vibrated by an ultrasonic generator 44 in axialdirection 45 (FIG. 2). The ultrasonic generators are configured to avoidor greatly minimize the production of non-axial forces which may bedetrimental to the bond pads 22. For example, piezoelectric basedultrasonic generators exist which have feedback sensors fornon-linearity compensation.

[0049]FIG. 3 shows a bare die 14 and an interconnect 24 wherein raisedcontact members 30 on the interconnect are joined to bond pads 22 of thedie. The tips 62 of the apexes 52 of the contact members 30 have piercedthe oxide layer 54 and penetrated the metal 58 of the bond pads 22 to a“full penetration depth” 70. The full penetration depth 70 is less thanthe bond pad thickness 78.

[0050] The method of simultaneously forming effective bonds between abare die 14 with bond pads 22 and an interconnect 24 with raised contactmembers 30 is as follows:

[0051] (a) the die 14 and interconnect 24 are mounted in alignment in anassembler or similar machine 10 designed to simultaneously connect theplurality of corresponding contact members and bond pads with acombination of simple compression and ultrasonic vibration;

[0052] (b) the active surface 20 of the die 14 and the connectionsurface 28 of the interconnect 24 are brought together whereby eachcontact member 30 is aligned with a corresponding bond pad 22 foraccurate connection;

[0053] (c) while compressing the die 14 and interconnect 24 together ata relatively low force, the die and/or interconnect is/areultrasonically vibrated with a short burst of generally linear,axially-directed vibrational energy to cause the tips 62 of the apexes52 of the interconnect to pierce the oxide layer 54 on the bond pads 22and penetrate the underlying metal 58 to the desired full penetrationdepth 70.

[0054] If the purpose of joining the die 14 and interconnect 24 is toperform a brief test, the compression force (but not the ultrasonicvibration) may be continued until the test is complete. The die 14 andinterconnect 24 may then be pulled apart, either with or without theapplication of ultrasonic energy. In general, however, the bondingresulting from the invention is adequate to permit withdrawal ofcompressive forces during testing and to produce bonds capable ofpermanence.

[0055] Turning again to FIG. 4, force-penetration curve 80 representsthe effect of using ultrasonic force to pierce the oxide layer 54 at amuch reduced applied force 82 (as compared to force 66). Ultrasonicvibration continued through the metal penetration portion of the curve80 significantly reduces the compressive forces required for fullpenetration. Thus, curve 80 is seen to be at a much lower level ofcompression force than curves 64 and 74 of the prior art. Fullpenetration is achieved at the compression force level 84.

[0056] The invention has been illustrated herein using an interconnect24 of a particular configuration. However, the invention is applicableto an interconnect with any puncture-type raised contact member. Theterm “interconnect” encompasses any substrate with such contact membersformed thereon, and may include test probes, interposers, etc.

[0057] The benefits of the invention include a lower tendency towardtearing of the bond pads 22, very rapid bonding of all pads 22, andgreater reliability of the bonding. It is believed that the methodreduces the possibility of damage to the piercing members, e.g. apexes52, of the contact members, thereby permitting greater repeated use ofthe interconnect 24.

[0058] It is apparent to those skilled in the art that various changes,additions and modifications may be made in the improved die-substrateinterconnection method and apparatus as disclosed herein withoutdeparting from the spirit and scope of the invention as defined in thefollowing claims.

What is claimed is:
 1. A method for forming a connection comprising:providing a semiconductor die having a bond pad on a surface thereof;providing an interconnect having a contact member on a connectionsurface thereof, said contact member for penetrating a layer of materialon an outer surface of said bond pad for connecting said contact memberto said bond pad of said semiconductor; bringing together said firstsurface of said semiconductor die and said connection surface of saidinterconnect having said contact member aligned proximate said bond padon said first surface of said semiconductor die; engaging saidsemiconductor die and said interconnect using a force; and substantiallyultrasonically vibrating one of said semiconductor die and saidinterconnect using vibrational energy having said contact member of saidinterconnect penetrating a portion of said bond pad of saidsemiconductor die forming an electrical connection.
 2. The method ofclaim 1, whereby said engaging and said ultrasonic vibration arecontinued having said contact member penetrating said portion of saidbond pad to a predetermined depth.
 3. The method of claim 2, whereinsaid predetermined depth comprises a range of about 0.3-0.8 of athickness of said bond pad.
 4. The method of claim 2, wherein saidultrasonic vibration is conducted to achieve a vibrational amplitude inthe range of about 5 to about 30 percent of said predetermined depth. 5.The method of claim 1, wherein said ultrasonic vibration is conducted inthe range of about 5 to about 200 milliseconds.
 6. The method of claim2, further comprising: detecting penetration of said bond pad to saidpredetermined depth by detection/feedback apparatus.
 7. The method ofclaim 6, further comprising: terminating said penetration of said bondpad on said surface of said semiconductor die by detecting saidpenetration of said bond pad to said predetermined depth by saiddetection/feedback apparatus.
 8. The method of claim 1, wherein saidelectrical connection comprises a non-permanent electrical connectionbetween said bond pad and said contact member.
 9. The method of claim 1,wherein said electrical connection comprises a permanent electricalconnection between said bond pad and said contact member.
 10. The methodof claim 1, further comprising: retracting said semiconductor die andsaid interconnect from each other during application of a linear axialultrasonic vibrational force to one of said semiconductor die and saidinterconnect, said retracting for disconnecting said semiconductor diefrom said interconnect.
 11. A method for forming connections comprising:providing a semiconductor die having a bond pad on a surface thereof;providing an interconnect having a contact member on a connectionsurface thereof, said at least one contact member for penetrating alayer of material on an outer surface of said bond pad for connectingsaid contact member to said at least one bond pad of said semiconductordie; bringing together the surface of the semiconductor die and theconnection surface of the interconnect having said contact memberaligned proximate said bond pad on said surface of said semiconductordie; engaging said semiconductor die and said interconnect by applying aforce; and substantially ultrasonically vibrating one of saidsemiconductor die and said interconnect using vibrational energy havingsaid contact member of said interconnect penetrating a portion of saidbond pad of said semiconductor die forming an electrical connection. 12.The method of claim 11, whereby said engaging and said ultrasonicvibration are continued having said contact member penetrating saidportion of said bond pad to a predetermined depth.
 13. The method ofclaim 12, wherein said predetermined depth comprises a range of about0.3-0.8 of a thickness of said bond pad.
 14. The method of claim 12,wherein said ultrasonic vibration is conducted to achieve a vibrationalamplitude in the range of about 5 to about 30 percent of saidpredetermined depth.
 15. The method of claim 11, wherein said ultrasonicvibration is conducted in the range of about 5 to about 200milliseconds.
 16. The method of claim 12, further comprising: detectingpenetration of said bond pad to the predetermined depth bydetection/feedback apparatus.
 17. The method of claim 16, furthercomprising: terminating the penetration of said bond pad on said surfaceof said semiconductor die by detecting the penetration of said bond padto the predetermined depth by said detection/feedback apparatus.
 18. Themethod of claim 11, wherein said electrical connection comprises anon-permanent electrical connection between said bond pad and saidcontact member.
 19. The method of claim 11, wherein said electricalconnection comprises a permanent electrical connection between said bondpad and said contact member.
 20. The method of claim 11, furthercomprising: retracting said semiconductor die and said interconnect fromeach other during application of a linear axial ultrasonic vibrationalforce to one of said semiconductor die and said interconnect, saidretracting for disconnecting said semiconductor die from saidinterconnect.